Beneficiation of apatite-calcite ores



United States Patent Office 3,259,242 Patented July 5, 1966 3 259 242 BENEFICIATION F AfiATITE-CALCITE ORES Robert E. Snow, Lakeland, Fla., assignor to International Minerals & Chemical Corporation, a corporation of New York No Drawing. Filed Nov. 29, 1962, Ser. No. 241,057

12 Claims. (Cl. 209-466) This invention generally relates to froth flotation beneficiation of minerals. In a particular aspect it relates to froth flotation benefication of calcitic phosphate ores. The novel process of this invention is applicable to the beneficiation of apatite ores containing calcite in which these minerals may be substantially completely liberated from each other and in which the apatite occurs as crystalline apatite.

Apatite is a common mineral and appears in small amounts in practically all igneous rocks. Concentrations rich enough to justify mining are found in many localities. The mineral apatite is a phosphate of lime containing varying amounts of chlorine, fluorine, carbonate and hydroxyl. The phosphorus pentoxide content usually ranges from 41 to 42 percent. The fluorine content has ranged as high as 3.8 percent but generally is about 3.3 percent.

For the major uses of apatite, the mineral is preferably in concentrated form. The phosphate industry requires, for the production of fertilizers, superphosphate, triple superphosphate and phosphoric acid, a phosphatic material of relatively high BPL content and irriposes price penalties where impurities are present in excess of certain maximum fixed percent-ages. The term bone phosphate of lime, commonly abbreviated to BPL, is generally used to express the phosphate content of fertilizers. It is the equivalent of Ca ('PO In the analysis of phosphatic materials, the chemist generally reports the phosphorus content in terms of phosphorus pentoxide (P 0 In order to be attractive on a commercial scale, a process for beneficiating a phosphate ore should produce a phosphate concentrate which is substantially free of gangue minerals. Many methods have been devised to beneficiate phosphate ores. Froth flotation beneficiation of phosphate minerals is commercially practiced on phosphate ores in which silicate minerals are the predominant gangue. Prior to the present invention, however, it has not been economically practical to beneficiate phosphate ores containing significant amounts of calcite. Calcite is calcium carbonate, CaCO CaO, 56.0%; CO 44.0%. It has been found to be particularly diflicult to beneficiate calcitic phosphate ores containing at least 2% by weight calcite. It has, however, now been discovered, and the present invention is in part based on this discovery, that calcitic-apatite ores may be efliciently beneficiated by froth flotation when the apatite is present as crystalline apatite.

Accordingly, it is an object of the present invention to provide a froth flotation process for beneficiating a calcitic phosphate ore.

It is another object of the invention to provide a froth flotation process for beneficiating a crystalline apatite ore containing at least 2% by weight calcite.

It is a more specific object of the invention to provide a froth flotation process for beneficiating a crystalline apatite ore containing siliceous gangue and at least 2% by weight of calcite gangue in which these materials may be substantially liberated from each other.

These and other objects and advantages of the present invention will be apparent as the description of the invention progresses.

In accordance with the present invention, it has been discovered that eminently satisfactory beneficiation of crystalline apatite ores and minerals containing calcite can be achieved by froth flotation in a series of critical and interdependent process steps.

In one embodiment, the present invention is a process for beneficiating a crystalline apatite material containing calcite and silicate mineral impurities which comprises subjecting a mixture containing discrete particles of crystalline apatite, calcite and silicate minerals to anionic flotation at a pH above 7.0 whereby crystalline apatite and calcite are floated, scrubbing the crystalline apatitecalcite floated material with a weak acid, subjecting the scrubbed crystalline apatite-calcite floated material to cationic flotation at a pH below 7.0 whereby the crystalline apatite is floated, and recovering a crystalline apatite concentrate.

Ores which may be beneficiated by the method of this invention are the natural crystalline apatite ores containing calcite and silicate minerals, and usually containing other gangue minerals. The apatite must, however, be in the crystalline form. Oolitic sedimentary apatite-calcitesilicate mineral deposits cannot be efliciently beneficiated iirthe process of this invention. It is true that the oolitic sedimentary apatite, such as exists in Florida pebble phosphate has a submicroscopic crystalline (cryptocrystalline) structure, however, to the naked eye it is generally oolitic and not crystalline and, in fact, some authorities call such material non-crystalline. In contrast, the apatite in igneous rocks and some metamorphic deposits has a crystalline structure visible to the naked eye. It is such crystalline apatite that is efiiciently beneficiated in the process of the present invention and to further distinguish it from sedimentary oolitic phosphate it may be denominated macrocrystalline apatite since it has a macrostructure.

Large deposits of macrocrystalline apatite ores containing calcite and silicate gangue minerals are found near Nemegos, Ontario, Canada, and large deposits are found in the Rocky Mountains and the Appalachian Mountains as well as in the Scandinavian region. Deposits are also found in South Africa.

In addition to the ores or natural mixtures of macrocrystalline apatite-calcite-silicate minerals, artificially created mixtures or concentrates obtained in various beneficiation processes may be beneficiated in the process of the present invention.

Regardless of source of the macrocrystalline apatitecalcite-silicate mixture, it is necessary that the macrocrystalline apatite values be substantially liberated from the calcite and silicate mineral gangue components of the mixture and be of a mesh size amenable to froth flotation operation. Accordingly, the material to be treated are, where necessary, reduced to a particle size of less than about 10 mesh and preferably to a particle size of less than about 20 mesh. The lower limit of particle size is about 325 mesh and desirably will be about 200 mesh, since 200 mesh phosphatic material is not effectively separated by froth flotation.

The liberated mixture containing discrete particles of macrocrystalline apatite, calcite and silicate minerals, is preferably washed to remove -44 micron slimes. Such desliming operations are well known in the phosphate mineral beneficiation industry. The deslimed liberated 3 mixture is then subjected to anionic flotation at a pH above 7.0.

The anionic flotation may employ any suitable anionic or negative ion flotation reagent. Many standard anionic flotation reagents are known to the art. The particular anionic reagent utilized in the anionic froth flotation does not constitute an essential feature of this invention which is operable with and contemplates all such reagents. Representative conventional anionic reagents comprise fatty acids or fatty acid soaps, particularly mixed fatty acids or soaps thereof; fatty acids or soaps derived from natural sources such as tall oils; fatty acids or soaps of acids derived from animal and vegetable oils and fats; esters of inorganic acids with high molecular Weight alcohols; and the like. Conventionally, such anionic reagents are used in solution, as an emulsion, or in a dispersion in a carrier medium such as a hydrocarbon oil, norm-ally kerosene or fuel oil. One widely used specific reagent combination comprises about one to about three parts tall oil, from about two to about four parts kerosene,

and from about two to about four parts bunker C fuel oil. The particulate mixture may be conditioned with the flotation reagent in conventional manner and in conventional amount. The flotation reagent is generally used in amount of from about 0.1 to about 5.0 lbs. of flotation reagent per ton of solids treated. Flotation depressant for siliceous materials may also be present in the flotation reagents. The use of such depressants is well known in the flotation art. Sodium silicate and quebracho are typical preferred depressants.

The anionic flotation should take place under alkaline conditions; that is the pH of the material during preconditioning and in the flotation cell should be above 7.0 and preferably is within the range of from about 7.2 to about 9.0. Basic materials, preferably sodium or ammonium hydroxide, are used to raise the pH to the desired level.

The reagentized mixture is subjected to froth flotation employing any suitable equipment. Standard flotation equipment or flotation cells are well known in the art.

The flotation is effective to remove in the overflow a substantial amount of the macrocrystalline apatite values of the mixture together with a substantial amount of the calcite particles. The underflow will contain a substantial portion of the silicate particles in the feed to the anionic flotation.

The froth float fraction from the anionic flotation is an intermediate concentrate containing a major portion of the macrocrystalline apatite in the feed to the anionic flotation and containing a substantially lower amount of silicate minerals as compared to the feed to the anionic flotation. The intermediate concentrate still contains a substantial and significant amount of calcite which is floated off with the macrocrystalline apatite.

In accordance with the present invention the intermediate concentrate is treated to remove the effect of the anionic flotation operation. The intermediate concentrate is preferably scrubbed with a weak aqueous acidic medium, preferably a Weak acid to remove the anionic flotation reagent from the intermediate concentrate. Scrubbing operations of the general type are well known in the flotation art. The scrubbing is, however, preferably with a weak acid, not a-strong mineral acid such as sulfuric acid which is conventionally used to scrub intermediate concentrates obtained in beneficiating Florida pebble phosphate.

The scrubbing may be with a weak acid, preferably sulfurous acid, or a combination of weak acids with or without an acidic metal salt, for example, aluminum sulfate, ferric chloride, etc. Sulfurous acid is preferred because it does not substantially dissolve apatite rapidly and is relatively inexpensive. Other relatively weak acids such as inter alia, oxalic acid, acetic acid, formic acid, and hypophosphorus acid may also be used. Although they are more diflicult to handle, nitrous acid and hypochlorous acid may also be used.

The treated intermediate macrocrystalline apatite fraction is then subjected to cationic flotation at a pH preferably below whereby macrocrystalline apatite is floated to provide a macrocrystalline apatite float concentrate containing a substantially lower amount of calcite as compared to the feed to said cationic flotation. The cationic flotation of macrocrystalline apatite is a unique feature of the process of the present invention. It will be apparent to those skilled in the art that other mixtures containing discrete particles of calcite and macrocrystalline apatite may be beneficiated by cationic flotation in accordance with the present invention. The present invention, accordingly broadly embraces cationic flotation of such mixtures whether they are derived from an anionic flotation operation, by other beneficiation process, or whether such mixtures are naturally occurring or artificially created. In a typical froth flotation operation as practiced on Florida pebble phosphate, silicate minerals are selec tively floated away from phosphate minerals, that is the phosphate reports to the underflow. The present flotation process is, accordingly, in direct contrast with such Florida operations since in the present process phosphate particles are floated and the calcite particles report to the underflow. In order to achieve separation by froth flotation of phosphate minerals from calcite, the phosphate mineral must be macrocrystalline apatite.

The intermediate macrocrystalline apatite fraction containing calcite, or other macrocrystalline apatite-calcite mixture, is subjected to cationic flotation employing any suitable cationic or positive ion flotation reagent. Many standard cationic flotation reagents and reagentizing or conditioning procedures are known to the art and may be used. The particular cationic reagent utilized in the cationic forth flotation does not constitute an essential feature of this invention which is operable with and contemplates all such cationic reagents. Such reagents include, inter alia, the higher aliphatic amines and their salts with inter-soluble acids; the esters of amino alcohols with high molecular weight fatty acids and their salts with inter-soluble acids; the higher alkyl-o-substituted isoureas and their salts with water-soluble acids; the higher aliphatic quaternary ammonium bases and their salts with water-soluble acids; the reaction product of polyalkylene polyamines with fatty acids and/ or fatty acid triglycerides; the higher alkyl pyridinium watersoluble acids; the higher alkyl quinolinium salts of watersoluble acids; and the like. In general, amine-type reagents, such as Cg-Clg amines and their salts with water-soluble acids, such as acetic acid, are preferred.

The cationic flotation is preferably effected at a pH below 7.0 and more preferably within the range of from about 5.0 to about 6.9. Any suitable acid may be used to lower the pH to below 7.0 and preferably to adjust the pH to Within the range of from about 5.0 to about 6.9. Sulfuric acid, sulphurous acid, hydrochloric acid, nitric acid, acetic acid, inter alia, may be used to adjust the pH.

Conventionally, such cationic reagents are used in solution, as an emulsion, or in a dispersion in a carrier medium such as a hydrocarbon oil, kerosene or fuel oil, No. 2 fuel oil commonly being used.

The intermediate concentrate may be conditioned with the cationic flotation reagent in conventional manner and conventional amout. The flotation reagent is generally used in amount of from about 0.1 to about 5.0 lbs. of flotation reagent per ton of solids conditioned.

The reagentized ore is subjected to cationic froth flotation again employing any suitable flotation equipment, many types of which are well known in the art. The flotation is effective to produce an overflow containing a substantial amount of the macrocrystalline apatite values of the ore. The macrocrystalline apatite float concentrate contains a substantially lower amount of calcite as compared to the feed to the cationic flotation.

Multiple stage cationic flotation is preferred to reject most of the calcite gangue. Specifically a rougher-cleaner or a rougher-cleaner-recleaner flotation are preferred.

In order to give a fuller understanding of the invention, but with no intention to be limited, thereto, the following specific examples are given.

The amine rougher froth was subjected to a cleaner and a recleaner flotation, with no additional reagent addi tion, to yield a final fertilizer-grade apatite concentrate. This concentrate, at an overall weight yield of 10.7%, assayed 72.2% BPL, 4.2% CO and 4.6% insol. repre- Lb./ ton ore NaOH 0.59 Arizona tall oil 1.58 Kerosene 1.58 Bunker C fuel oil 0.78

The reagentized ore was subjected to rougher flotation using 3.16 pounds of Na SiO per ton of ore for silicate mineral depression. The rougher froth was subjected to a cleaner flotation using an additional 0.79 pound of Na SiO per ton of ore. The cleaner concentrate, at a weight yield of 17.6%, assayed 50.2% BPL representing an overall BPL distribution of 86.5%. At this stage, the carbonate mineral content of the fatty-acid concentrate was too high for use in fertilizer manufacture. Consequently, the fatty acid concentrate was scrubbed at about 35% solids for 5 minutes with 19.8 pounds of S per ton of ore (added as a 6% H SO solution), washed and dewatered, and scrubbed a second time with 3.95 pounds of H 80 per ton of ore, and washed and dewatered to yield a dereagentized product. The dereagentized fattyacid bulk concentrate was then subjected to amine flota- EXAMPLE I senting an overall BPL recovery of 75.6% A sample of calcitic phosphate ore from Finland had A material balance for the process is shown in the the following mineral composition: following Table 1.

Table 1 Assay, percent Distribution, percent Product Percent weight BPL 00, Insol. BPL CO2 Insol.

Finnish Phosphate:

Amine Reeleaner Cone 10. 7 72. 2 4. 2 4. 6 75. 6 11. 5 1. 4 Amine Recleaner Tail 0.9 35. 4 19. 3 9. 4 3.1 4. 4 0.2 Amine Cleaner Tail" 1. 3 22. 2 27. 7 6.7 2.8 9. 2 0. 3 Amine Rougher TaiL 4. 7 10.8 37. 4 2. 3 5. 0 45.1 0. 3 Fatty-Acid Cleaner Tail. 4. 6 9. s 9.1 as. 5 4. 3 10.8 4. 7 Fatty-Acid Rougher Tail 55.8 0. 4 0. 4 44. 0 2. 2 5. 6 69.3 -325 Mesh Slime e. 3 9.6 7. 5 so. 2 5. 9 12.1 5. 4 +35 Mesh Mica. 15. 7 0. 7 0. a 41. 4 1.1 1. 3 1s. 4

Composited Head 100. 0 10.2 3. 9 35. 4 100. 0 100.0 100.0

Percent EXAMPLE II 32 2;: A weathered calcitic phosphate ore from Transvaal,

South fri Dolomite u 35 A ca, had the following mineral composition Mica (biotite-phlogopite) 73 P r Ferromagnesian silicates, magnetite, and feldspar 7.5 Apafilte 20 Pyrite and pyrrhotite Trace 35 9 7 Diopside 63 100 Mica 10 A representative sample of the ore was stage crushed 100 to +6 mesh using a rollcrusher. The -6 mesh ore was 7 Stage ground to 8 35 m sh using aball mill. The A representative sample of the ore was stage rollcrushed to +8 mesh. The minus 8 mesh ore was screened at 35 mesh, and the +35 mesh fraction was stage ground in a ball mill to 35 mesh and combined with the 35 mesh screen undersize. The combined 35 mesh ore was deslimed by decantation at 325 mesh. The 35 +325 mesh sands, at a weight yield of 94.1%, contained 95.1% of the BPL values present in the ore. The deslimed sands were conditioned for 5 minutes at solids with the following reagents:

Lb./.ton ore NaOH 0.5 Arizona tall oil 1.6 Kerosene 1.6 Bunker C fuel oil 1.0

Lb./ton ore S0 (as 6% H SO solution) 6.3 Tallow amine acetate 0.18 Distilled rosin amine acetate 0.18 Kerosene 0.36

The amine rougher froth was subjected to a cleaner flotation to yield a final high-grade apatite concentrate. This concentrate, at an overall weight yield of 10.4%, assayed 79.4% BPL, 2.7% CO and 3.8% insol. representing an overall BPL recovery of 49.2%

A material balance for the process is shown in the following Table 2.

A material balance for the process is shown in the following Table 3.

Table 2 Assay, percent Distribution, percent Product Percent weight BPL C03 Insol. BPL CO2 Insol.

Transvaal Phosphate:

Amine Cleaner Cone 10. 4 79. 4 2. 7 3. 8 49. 2 12. 3 0.6 Amine Cleaner Tail 1. 9 2S. 3 23. 14. 8 3. 2 19.0 0.4 Amine Rouglier Tail-" 1. 6 7.4 33. 0 14. 3 0. 7 23. 0 0. 3 Fatty-Acid Rongher Ta 80. 2 8. 8 0. 9 80. 9 42. 0 30.7 93. 7 325 M Slime 5. 9 13. 9 5. 9 58.8 4. 9 15. 0 5. 0

Composited Head 100. 0 16. 8 2- 3 69. 2 100.0 100.0 100. 0

Table 3 Assay, percent Distribution, percent Product Percent weight BPL CO: nsol. BPL CO: Insol.

Ontario Phosphate:

Amine Recleaner Gone 35. 72. 3 2.6 8. 2 79.9 11.0 8. 1 Amine Reeleaner Tail 4. 8 13. 6 17. 8 5. 2 2.0 10.1 0.7 Amine Cleaner Tail 7. 0 4. 5 37. 4 1.4 1.0 31.0 0. 3 Amine Rougher Tai1- 8. 3 3. 7 42. 7 1. 1 1. 0 42.0 0.2 Fatty-Acid Rougher Tail 31.0 1. 7 0.3 95.6 1. 6 1.1 82.2 200 Mesh Slime 13. 4 34.8 3. 0 23. 0 14. 5 4.8 8.5

Composited Head 100.0 32. 1 8. 4 36.1 100.0 100.0 110. 0

3O Lb./ton feed S0 8.1 A sample of calcite-apatite rock from Ontario, Canada, P amule acelate had the following mineral composition: Dlstlned r0511] amme acetate percent Kerosene 0.44 p j 38 The amine rougher froth was subjected to a cleaner Calcite 7 and a recleaner flotation to yield a fertilizer grade apatite Mfflglletlte 3O concentrate. This concentrate, at an overall weight yield slhcates 1 of 35.5%, assayed 72.3% BPL, 2.6% 00 and 8.2% Pyrfhotlte 1/2 40 insol. representing an overall BPL recovery of 79. 9%. Pyrochlore /2 EXAMPLE IV 100 A sample of 28 +200 mesh apatite marble from Fin- Nepheline, zeolites, pyroxene, feldspar, biotite. land had the following mmeral composltlonl Percent A representative sample of the ore was stage com- Ap i 52 minuted to 35 mesh and deslimed at 200 mesh using al lt -d lomlte 43 essentially the same procedure described in Example II. The' 35/+200 mesh sands, at a weight yield of 86.6%, 100

contained 85.5% of the BPL values present in the ore.

The deslimed sands were conditioned at solids for d 4 minutes with the following reagents:

Lb./ton ore NaOH 0.87 Arizona tall oil heads 2.16 Kerosene 2.16 Bunker C fuel oil 0.87 N21 SiO 3.46

The tall oil heads had the following analysis:

Percent Fatty acid 82.9 Rosin acid 0.5 Unsaponifialbles 16.5 Ash and moisture 0.1

The reagentized ore was subjected to rougher flotation as in the previous examples. The fatty-acid concentrate, at a weight yield of 55.6%, assayed 48.4% BPL and contained 83.9% of the BPL values present in the ore. The fatty-acid concentrate was scrubbed for 2 minutes at about 35% solids with 16.9 pounds of S0 per ton of ore, washed and dewatered, and the process repeated. The dereagentized bulk concentrate was subjected to amine flotation using the following reagents:

The sample was subjected to a rougher-cleaner-recleaner amine flotation using the following reagents added to the rougher stage:

Ace-tic acid 4.2

55 Fatty amine 0.53 Kerosene 1.06

The final recleaner concentrate, at an overall weight yield of 44.2%, assayed 83.5% BPL and 3.7% CO rep esenting an overall BPL recovery of 84.0%

1 Dilute HNOs insol. includes magnetite.

The above examples illustrate that a high recovery of macrocrystalline apatite values may be achieved in accordance with the present invention. The process is economical and represents a novel process.

The description of the invention utilized specific reference to certain details; however, it is to be understood that such details are illustrative only and are not given with the intention of limiting the scope of the invention. Other modifications and equivalents of the invention will be apparent to those skilled in the art from the foregoing description.

Having now fully described and illustrated the invention, what is desired to be secured and claimed by Letters Patent is set forth in the appended claims.

We claim:

1. A froth flotation process for beneficiating a macrocrystalline apatite-calcite mixture which comprises subjecting a mixture containing discrete particles of macrocrystalline apatite and calcite to cationic flotation at a pH below 7.0, and separately collecting a macrocrystalline apatite, as a float concentrate containing a substantially lower amount of calcite as compared to said mixture and a tailing containing a substantially higher amount of calcite as compared to said mixture.

2. The process of claim 1 wherein said macrocrystalline apatite-calcite mixture contains at least 2% by weight calcite.

3. The process of claim 1 wherein said discrete particles are substantially all of mesh size.

4. The process of claim 1 wherein said cationic flotation is eflected at a pH within the range of from. about 5.0 to about 6.9.

5. The process of claim 1 wherein said cat-ionic flotation is eifected in the presence of an amine-type cationic flotation reagent.

6. A froth flotation process for beneficiating a macrocrystal-line apatite-silica-calcite mixture which comprises subjecting a mixture containing discrete particles of macrocrystalline apatite, calcite and silicate minerals to anionic flotation at a pH above 7.0, collecting an intermediate macrocrystalline apatite float fraction containing calcite and a substantially lower amount of silicate mineral-s as compared to the feed to said anionic flotation, treating said intermediate fraction with a weak acid to remove said anionic flotation reagent, subjecting the treated intermediate fraction to cationic flotation at a pH below 7.0, and separately collecting a macrocrystalline apatite as a float concentrate containing a substantially lower amount of calcite as compared to the feed to said cationic flotation and a tailing containing a substantially higher amount of calcite as compared to the feed to said cationic flotation.

7. The process of claim 6 wherein said mixture contains at least 2% by Weight calcite.

8. The process of claim 6 wherein said discrete parti cles are substantially all of 20 mesh size.

9. The process of claim 6 wherein said cationic flotation is effected at a pH within the range of from about 5.0 to about 6.9.

10. The process of claim 6 wherein said anionic flotation is effected at a pH within the range of from about 7.2 to about 9.0.

11. The process of claim 6 wherein said cationic flotation is effected in the presence of an amine-type cationic flotation reagent.

12. The process of claim 6 wherein said anionic flotation is effected in the presence of a tall oil anionic flotation reagent.

References Cited by the Examiner UNITED STATES PATENTS 2,105,807 1/1938 Crago 209-167 2,158,220 5/1939 Crago 209-167 2,313,360 3/1943 Ralston 209-166 2,959,281 11/ 1960 Faucher 209166 3,039,197 5/1962 Northcott 209166 3,063,561 11/1962 Snow 209-127 FOREIGN PATENTS 859,155 1/1961 Great Britain.

HARRY B. THORNTON, Primary Examiner.

HERBERT L. MARTIN, Examiner.

R. HALPER, Assistant Examiner. 

1. A FROTH FLOTATION PROCESS FOR BENEFICIATING A MACROCRYSTALLINE APATITE-CALCITE MIXTURE WHICH COMPRISES SUBJECTING A MIXTURE CONTAINING DISCRETE PARTICLES OF MACROCRYSTALLINE APATITE AND CALCITE TO CATIONIC FLOTATION AT A PH BELOW 7.0, AND SEPARATELY COLLECTING A MACROCRYSTALLINE APATITE, AS A FLOAT CONCENTRATE CONTAINING A SUBSTANTIALLY LOWER AMOUNT OF CALCITE AS COMPARED TO SAID MIXTURE AND A TAILING CONTAINING A SUBSTANTIALLY HIGHER AMOUNT OF CALCITE AS COMPARED TO SAID MIXTURE. 